A generalized in-phase/quadrature-phase receiver uses two mixers to demodulate a composite signal with magnitude and phase information into an in-phase component and a quadrature component. A first mixer receives the composite signal and an in-phase local oscillator signal and mixes these two signals together to produce a first down-converted signal. A second mixer receives the composite signal and a quadrature-phase local oscillator signal and mixes these two signals together to produce a second down-converted signal. The first down-converted signal is processed by a first low-pass filter to remove unwanted high-frequency portions, leaving the desired in-phase component, and the second down-converted signal is processed by a second low-pass filter to remove unwanted high-frequency portions, leaving the desired quadrature component.
Under ideal conditions, the first mixer and the first low pass filter supply an equal amount of gain to the in-phase component, as the second mixer and second low pass filter supply to the quadrature component. In actual practice, however, factors such as manufacturing process non-idealities, temperature, and supply voltage can cause a gain imbalance between these two branches (i.e., between the first mixer and the first low pass filter, which comprise a first branch, and the second mixer and the second low pass filter, which comprise a second branch).
A gain imbalance between the two branches can be reduced by comparing the average power of the in-phase component produced by the first branch and the average power of the quadrature phase component produced by the second branch and then using this information to adjust the gain of one or both branches. However, conventional approaches used to determine the average power of the in-phase component and the quadrature component typically require a relatively large amount of processing power, which can be costly in terms of the amount of hardware needed. This is especially true in in-phase/quadrature-phase receivers that use sigma-delta analog-to-digital conversion.
Therefore, what is needed is an apparatus for determining the average power of the in-phase component and quadrature component that is less costly in terms of hardware as compared to the conventional approaches.
The present invention will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.